Verkruysse et al., “Remote plethysmographic imaging using ambient light”, Optics Express, 16 (26), 22 Dec. 2008, pp. 21434-21445 demonstrates that photoplethysmography signals can be measure remotely on the human face with normal ambient light as the source and a simple digital, consumer-level photo camera in movie mode. After setting the camera in movie mode, volunteers were asked to sit, stand or lie down to minimize any movements. Color movies were saved by the camera and transferred to a personal computer. Pixel values for the red, green and blue channels were read for each movie frame, providing a set of PV(x,y,t), where x and y are horizontal and vertical positions, respectively and t is time corresponding to the frame rate. Using a graphic user interface, regions of interest (ROI) were selected in a still (selected from the movie) and the raw signal PVraw(t) was calculated as the average of all pixel values in the ROI. Fast Fourier Transforms were performed to determine the power and phase spectra. A phase map for the heart rate frequency of 1.43 Hz is shown in one of the figures. The article mentions that the authors tried briefly to use a telelens in combination with one of their cameras, because there is interest in remote sensing of the heart rate for combat triage or for athletic monitoring purposes.
Applications of photoplethysmography known from the prior art are limited to diagnostics using heart rate and respiration determinations and using imaging.